It is often difficult to navigate flexible cardiac leads through tortuous vasculature for implantation within the vasculature or the heart. The deformable nature of some leads makes it difficult to push the lead through the twisting vasculature with a stylet. The leads bend unpredictably and lodge within the veins and arteries. Additionally, leads often include fixation features that snag on the vasculature or provide a larger profile during navigation. Leads with fixation features sometimes require multiple stylets to try navigation of the lead around corners or the like. The procedures are further complicated by enlarging the outer perimeter of leads to accommodate stylet lumens. Such lumens are often defined by coiled conductors that extend through the lead to couple with electrodes. The coiled conductors and the lumens take up space within the lead and enlarge the lead profile. Navigation of larger leads is complicated especially in tortuous vasculature, such as around the left side of the heart.
One example of an arrangement for implanting a lead is shown in U.S. Pat. No. 5,902,331. The apparatus described includes a lead having fixation features at the distal end. The lead is coupled to a guide body and moved along the guide body with a pusher wire. The fixation features of the lead are one disadvantage of this arrangement. Navigating the lead through vasculature, such as around the left side of the heart is difficult because the fixation features can undesirably lodge in vasculature tissue prior to reaching the desired implantation location. Additionally, the pusher wire is constrained from lateral movement at the distal end of the lead. If the lead becomes lodged within the vasculature the pusher wire can bow proximally to the distal end and aggravate the tissues of the vasculature. With the use of an introducing catheter around the entire arrangement the pusher wire is constrained from bowing to some extent, however the introducer catheter undesirably increases the outer perimeter of the apparatus and complicates navigation of the lead through vasculature.
Another example of an arrangement for implanting a lead is shown in U.S. Pat. No. 6,129,749. The apparatus includes a molded support body for a guide wire. The lead includes a lumen within the elongated lead body sized and shaped to receive a stylet. The stylet is used to move the lead over the guide wire into a desired orientation. One disadvantage of this arrangement is the elongated lead body is enlarged to accommodate the stylet. The lumen for the stylet is defined by a helically wound coil. The lumen and the wound coil increase the outer perimeter of the lead and navigation of the larger lead is complicated within tortuous vasculature.
U.S. Pat. No. 6,129,750 shows another example of an arrangement for implanting a lead. The apparatus includes a coil that has a naturally non-linear shape. The coil is deployed through a lumen of an over-the-wire lead and constrained from assuming the non-linear shape. When positioned where desired, the coil is released to assume the non-linear shape and engage the lead against the vessel wall. A disadvantage of this arrangement is that a coil has a relatively thick profile that is difficult to navigate through tortuous vasculature. Additionally, the coil is not securely engaged to the lead to permit rotation of the coil along with the lead to enhance contact with a desired surface within the vasculature (e.g., the myocardium of a heart).
What is needed is an assembly for positioning leads that overcomes the shortcomings of previous designs. What is further needed is an assembly capable of positioning leads and fixation devices within torturous vasculature.